1. Field of the Invention
The present invention relates to a vertical-position welding method, and more particularly, to a welding technique for welding butted edges of a pair of thick steel plates together in a vertical position.
2. Description of the Related Art
In shipbuilding sites or bridge construction sites, a vertical-position welding method is generally adopted in which butted edges of a pair of steel plates are welded together by a welder in a vertical position.
As such vertical-position welding, an electrogas arc welding method has been known in which a pair of steel plates are welded together by a single welding pass in the width direction of the plates (see Unexamined Japanese Patent Publication No. H11-254131 and “Patent Maps Classified by Technical Fields” from the Japan Patent Office, Machinery 3: Arc Welding Technology, 1.3.6 Electrogas Arc Welding Method).
Also, as common welding methods, multi-layer welding is known wherein a pair of steel plates are welded together by multiple passes of MAG or MIG welding in the width direction of the plates.
Meanwhile, as a result of the recent tendency toward larger-scale steel structures used in ships, bridges and the like, steel plates with greater thickness have come to be used.
In the case of using the electrogas arc welding, which essentially requires large heat input, to weld such thick steel plates, the heat input needs to be increased to an even higher level. Consequently, a wider region of the weld deteriorates in performance, giving rise to a problem that the weld fails to retain sufficiently high toughness, that is, mechanical strength.
Thus, to permit the electrogas arc welding to be applied to thick steel plates, attempts have been made to use steel products specially prepared for large heat-input welding, as such thick steel plates, thereby ensuring high mechanical strength.
However, the use of steel products specially prepared for large heat-input welding leads to substantial increase in costs and is not desirable.
The multi-layer welding method using MAG or MIG welding does not require large heat input and thus can be suitably applied to ordinary steel plates. Since the groove generally used in steel structures is a single V groove, however, the cross-sectional area of the groove is large, requiring much time for the construction of steel structures and significantly lowering the productivity.